1. Field of the Invention
The invention relates to a method of measuring a defocusing distance of light shined on a semiconductor wafer when exposing the semiconductor wafer with a resist applied thereto to the light, and a method of obtaining correct focusing of the light shined on the semiconductor wafer. This application is a counterpart application of Japanese application, Serial Number 206653/2002, filed Jul. 16, 2002, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
When a semiconductor wafer with a resist applied thereto is exposed to light with the use of a pattern exposure system, exposure is implemented by focusing the light on the semiconductor wafer. In this case, the semiconductor wafer in a state as placed on a stage of the pattern exposure system is exposed to the light, and consequently, there occurs a delicate deviation in focus for respective regions (hereinafter referred to as respective shots) of the semiconductor wafer due to inclination of the stage or unevenness of the top surface of the semiconductor wafer, so that there is the need for obtaining correct focusing on a shot-by-shot basis.
In order to obtain correct focusing, it is necessary to measure a defocusing distance for every shot. In the past, the defocusing distance used to be measured with a focusing sensor attached to a pattern exposure system. Measurement of the defocusing distance by use of the focusing sensor has been made, for example, as follows; first, light passing through a first aperture fixedly disposed is shined on a semiconductor wafer. Subsequently, the light falling on, and reflected from the semiconductor wafer is shined on a second aperture fixedly disposed. Because an optical path of the light reflected varies depending on the position of the semiconductor wafer, the amount of light passing through the second aperture as well undergoes variation. A defocusing distance in respective shots of the semiconductor wafer, reflecting the light, is calculated from the amount of the light passing through the second aperture on the basis of the amount of light passing through the second aperture when the semiconductor wafer is at a focus position.
Correct focusing is achieved by adjusting the position of the stage on which the semiconductor wafer is placed on the basis of the defocusing distances found by use of the focusing sensor.
With a conventional method of measurement, however, it is difficult to examine in which way there has occurred a deviation in focus, upward or downward, if the deviation in focus is only slight.
It is therefore an object of the invention to provide a method of measuring a defocusing distance and a method of obtaining correct focusing, whereby such a problem as described can be resolved.